Etymology
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rodent (n.)

"a rodent mammal" 1835 (as an adjective 1833), from Modern Latin Rodentia, the order name, from Latin rodentem (nominative rodens), "the gnawers," present participle of rodere "to gnaw, eat away," which is of uncertain etymology, possibly is from an extended form of PIE root *red- "to scrape, scratch, gnaw." Uncertain connection to Old English rætt (see rat (n.)). They are characterized by having no canine teeth and strong incisors.

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erose (adj.)
of a leaf, an insect wing, etc., "with indented edges that appear as if gnawed," 1793, from Latin erosus, past participle of erodere "gnaw away" (see erode).
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*red- 

*rēd-, Proto-Indo-European root meaning "to scrape, scratch, gnaw."

It forms (possibly) all or part of: abrade; abrasion; corrode; corrosion; erase; erode; erosion; radula; rascal; rase; rash (n.) "eruption of small red spots on skin;" raster; rat; raze; razor; rodent; rostrum; tabula rasa.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit radati "scrapes, gnaws," radanah "tooth;" Latin rodere "to gnaw, eat away," radere "to scrape;" Welsh rhathu "scrape, polish."

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gn- 
consonant cluster at the head of some words; the -g- formerly was pronounced. Found in words from Old English (gnat, gnaw), in Low German, and Scandinavian as a variant of kn- (gneiss), in Latin and Greek (gnomon, gnostic) and representing sounds in non-Indo-European languages (gnu).
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trout (n.)
Old English truht "trout," in part from Old French truite, both from Late Latin tructa, perhaps from Greek troktes "a kind of sea fish," literally "nibbler," from trogein "to gnaw," from PIE *tro-, from root *tere- (1) "to rub, turn." In late 17c. slang, trusty trout was used in a sense of "confidential friend."
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chaff (n.)

"husks of wheat, oats, or other grains," Old English ceaf "chaff," probably from Proto-Germanic *kaf- "to gnaw, chew" (source also of Middle Dutch and Dutch kaf, German Kaff), from PIE root *gep(h)- "jaw, mouth" (see jowl (n.1)). Used figuratively for "worthless material" from late 14c.

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gangrene (n.)

"putrefaction or necrosis of soft tissues," 1540s, cancrena, from Latin gangraena (Medieval Latin cancrena), from medical Greek gangraina "an eating or gnawing sore," literally "that which eats away," a dissimilated, reduplicated form of gran- "to gnaw," from PIE root *gras- "to devour" (see gastric).

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gastric (adj.)
1650s, from Modern Latin gastricus, from Greek gaster (genitive gastros) "stomach, paunch, belly," often figurative of gluttony or greed, also "womb, uterus; sausage," by dissimilation from *graster, literally "eater, devourer," from gran "to gnaw, eat," from PIE root *gras- "to devour" (source also of Greek grastis "green fodder," Latin gramen "fodder, grass," Old English cærse "cress").
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troglodyte (n.)

"cave-dweller," 1550s, from French troglodyte and directly from Latin troglodytae (plural), from Greek troglodytes "cave-dweller, cave-man" (in reference to tribes identified as living in various places by ancient writers; by Herodotus on the African coast of the Red Sea), literally "one who creeps into holes," from trogle "hole, mouse-hole" (from trogein "to gnaw, nibble, munch;" see trout) + dyein "go in, dive in" (see ecdysiast). Related: Troglodytic.

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scurf (n.)

late Old English scurf, "scaly or flaky matter forming on the surface of the skin," also "exfoliated epidermis," earlier sceorf, from Proto-Germanic *skurf- (source also of Old Norse skurfottr, Danish skurv, Swedish skorv, Middle Dutch scorf, schorf, Dutch schurft, Old High German scorf, German Schorf "scurf"), which probably is related to Old English sceorfan "to gnaw," scearfian "to cut into shreds" (from PIE *skerp-, from root *sker- (1) "to cut"). The form of the word likely is influenced by Scandinavian cognates. The scruff in scruffy is from a variant form.

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